You could always buy a DP and a AP and go stage 2 for a bit. Stage 2 basically like lighting a fire under stage 1's ass. the power difference is huge and it made my wrx alot more fun to drive around town. I really want to take it to the drag strip and see what i can do there. Ive spun my front tires on a shift from first to second on a dry, hot day once and that made me smile. But it could be bcause my tires are getting bald lol. Still, your going to need a DP anyways, and your tunner will be able to give you a pro tune with the AP you buy and that way you can save it on your PC and have it for ever and have the ability to switch to a less agressive tune if need be. I plan on going with the VF39 swap and would like to hit 300whp but like everyone says, its just a number. Well damnit i wana brag to all my friends on myspace with honda's that are dynoed at 350whp lol... Not like it matters because i take them from the dig everytime like nothing right now heh. Sorry got off topic there, but you should give stage two a try first. IMO going from stock which is about 165whp to stage 4 which is in the neighberhood of 285-300whp would be stupid. You wont know how to drive the damn car let alone controll it unless you have a pretty big racing back ground or something... Try out stage 2 for a while, get use to it and when the time comes go for that 300awhp mark. Good luck with your decision/build.

well im allready geting all that stuff (sti intercooler, 4"dp, vf39) and its not like im gona romp around once i get it tuned cause i realize that with all that power i gota take things slow and be able to control it. im not worried about going from stock to stage III it will be alot of fun is what it will be. plus ive driven my friends stage III wrx and i didnt have much problem controlling it. all i know is by the end of this weekend ill have alot more ponies in my wrx and i cant wait

Most of the time, "4 inch downpipe" refers to a bellmouth-style downpipe. The opening at the top of the pipe sort of resembles a bell (for lack of a better term) and the larger part of it actually connects to the back of your turbo with five bolts. The widest part of that oval-shaped opening is approximately four inches (measured horizontally). Most of the time, that four inch opening will gradually taper down to 3" by the time the pipe connects to the cat back. Sometimes people just like to say they have a 4" downpipe so it sounds bigger, but it could be considered either 3" or 4" depending how you look at it. Here's a picture to help illustrate what I'm talking about:

your gonna have a hard time reaching your 300+ target without running more than your planning. i, for example, am running the vf39, full turbo back, tgv deletes, inlet, intake, spearco tmic, and water/meth injection with a protune and i made 305/350 whp/tq at sea level and 301/356 whp/tq up at my elevation, which is about 5,000 ft. and the only reason i broke into the 300 mark is because of the water/meth injection. but honestly its not all about numbers. my buddy has an 07 wrx with a slightly bigger turbo and tuned by the same guy and he put down 267/255 whp/tq and he's dead even with me and then starts to pull.